Carbon debt results from carbon dioxide and other greenhouse gases released when land is converted from natural vegetation to agriculture. It’s called debt because until a new biofuel crop creates enough renewable fuel to offset the lost CO2, the new biofuel crop has no climate benefit.

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In fact, it’s the same as burning fossil fuel as far as the atmosphere is concerned, says Ilya Gelfand, postdoctoral researcher at Michigan State University who worked with the Great Lakes Bioenergy Research Center.

“Conversion creates carbon debt, which must be paid off before the biofuel crop can provide climate mitigation benefits,” he says. “No-till practices (planting without plowing) reduced by two-thirds the amount of debt created by the conversion, but still it would take 29 to 40 years for it to be repaid by growing corn and soybean for biofuel.”

“The conversion of CRP lands to corn and soybean production has a larger climate consequence than has been previously estimated,” Gelfand says. “And much of the debt comes from the loss of soil carbon that would have been stored in CRP land in the future had it not been converted.”

Nationally, more than 30 million acres are set aside as CRP land, and they provide significant climate, wildlife, and other conservation benefits, says co-author Phil Robertson, professor of crop and soil sciences.

“Growing CRP grasses rather than using the land for corn or corn-soybean production could maintain these benefits indefinitely while providing a valuable bioenergy feedstock,” he says. “It could be a win-win for farmers and the environment once a market for cellulosic biofuel develops.”

Researchers from the University of Toledo contributed to the study that was funded by the National Science Foundation. The GLBRC is a collaboration between Michigan State and the University of Wisconsin.